One-third of US adults are low-income and age earlier than their higher income peers, but it is not clear if increasing available household income could improve their health. Earlier aging is believed to be due, in part, to financial stress, or stress induced by insufficient income for basic needs. However, physiologic response to financial stress is untested. Research in this area requires knowledge of both health disparities and biology of aging and poses unique methodological challenges. Since it is not possible to randomly assign adults to differing income or financial stress levels, innovative methodologies must be used to evaluate their effect. The proposed research outlines three natural experiments leveraging existing physiologic biomarker data from population-based samples to ask distinct, but related, questions testing the theoretical concept of ?weathering? over the adult life-cycle. The first experiment tests the hypothesis that stress-sensitive biomarkers are higher during times of higher routine end-of-the-month financial stress in low-income older adults aged 70-79 by capitalizing on biomarker data from the Health, Aging and Body Composition Study and monthly Social Security payment timing. The second experiment quantifies cortisol response to a non-routine source of financial stress (i.e. an event that poses a risk to an individual?s financial situation) in low-income middle-aged adults, using MIDUS II data, based on four days of repeated cortisol samples and daily diary data, accounting for confounding. The third experiment exploits 2009 policy changes that expanded Supplemental Nutrition Assistance Program (SNAP) eligibility and benefits (participation increased 3% and benefits increased 16%) for some, but not all, lowincome adults to test stress- and nutrition-sensitive biomarker response to increased income. Biomarker changes over time will be compared in young and middle-aged low-income adults aged 18-59 who likely were and were not eligible for increased income. Within the fertile and well-suited environment of Johns Hopkins University, the application proposes training to (1) add biology of aging knowledge to my existing health disparities knowledge, enabling me to respond to an NIA priority area by conducting innovative research at the intersection of these two fields of study, and (2) add training developing and evaluating natural experiments using traditional clinical trial methods, causal inference and econometric modeling to my existing epidemiologic training, equipping me to independently investigate non-randomized exposures, such as income and financial stress, and develop effective interventions to improve the lives of low-income adults. The proposed research and training respond to NIA?s call to elucidate mechanisms contributing to disparities across the life-cycle.